1. Field of the Invention
The present invention relates to a biological tissue equivalent phantom unit (phantom unit) used by a specific absorption rate measuring system for evaluating absorption of electromagnetic wave energy; a specific absorption rate measuring system using the phantom unit; and a method thereof.
2. Description of the Related Art
In recent years and continuing, requirements are increasing for quantitatively evaluating a thermal effect caused by an electromagnetic wave emitted by a wireless radio transmitter; and a system that is capable of accurately and swiftly measuring a specific absorption rate (SAR), which is an index of the reaction of the electromagnetic wave on a living body, such as a human, is desired.
A SAR value is proportional to an electric field (|E|2), and is often used for evaluating the energy absorbed by a human body when a cellular phone is used near the human body, SAR being defined by the following Equation 1.SAR=σ|E|2/ρ  [Equation 1]
Here, σ and ρ represent conductivity [S/m] and density [kg/m3], respectively, of the biological tissue equivalent phantom.
Usually, when measuring SAR, an electric-field measuring method is used, wherein a short dipole detects an electric field generated in a medium (live body), which electric field is converted into SAR using Equation 1.
FIG. 1 shows a conventional specific absorption rate measuring system 100 that includes                a simulated body (phantom) 101 that simulates an electric constant of a human body with liquid,        a container 102 into which the liquid is provided,        a probe 103 for detecting an electric field,        a probe scanner 104,        a signal cable 105,        an electric field detection apparatus 106, and        a processor apparatus 107 for measurement operations and data analysis.        
Here, the electric field generated in the phantom is measured by arranging a measuring target instrument 108, such as a cellular phone, near the specific absorption rate measuring system 100 as shown in FIG. 1. The probe 103 for detecting the electric field is scanned in three dimensions by the probe scanner 104, and SAR is measured.
FIG. 2 shows another specific absorption rate measuring system 200 that includes                a phantom 121 that simulates the electric constant of the human body with a solid-state object,        a probe 122 for detecting the electric field,        a cable 123 for signal transmissions,        an electric-field detection apparatus 124,        a processor apparatus 125 for measurement operations and data analysis, and        a scanner 126.        
The electric field generated in the phantom is measured by arranging a measuring target instrument 127, such as a cellular phone, near the specific absorption rate measuring system 200 as shown in FIG. 2. However, unlike the conventional example shown by FIG. 1, the cellular phone 127 is moved by the scanner 126, and SAR is measured.
In either of the conventional examples, the probe 103 or 122, as applicable, for detecting the electric field is required. Each of the probes 103 and 122 for detecting the electric field includes a detecting element 110 as shown in detail on the right-hand side of FIG. 1. There, an electric field is detected by short dipole elements 111 and 112. Then, the electric field is detected by a Schottky diode 113 inserted in a gap, and a detected result in the form of an electrical signal is provided to the corresponding electric-field detection apparatuses 106 and 124 through high resistance wires 114. That is, the Schottky diode 113 detects a voltage generated by the short dipole elements 111, 112 formed with conductors, the length of which is about 2 to 5 mm.
However, since the short dipole antenna and the high resistance wires, both being conductive, are present in the electric field to be measured, the electromagnetic field distribution near the detecting element 110 is disturbed. This is a problem of the electric-field measuring method. Further, since it is difficult to reduce the length of the dipole elements 111, 112, it is expected that the disturbance will become greater as the frequency becomes higher.
Then, in an attempt to reduce the disturbance to the electromagnetic field generated by the measuring target 108, 127 (e.g. a cellular phone), the disturbance being due to the probe 104, 122 for detecting the electric field, an electric-field sensor 300 using an optical waveguide type modulator and a laser beam has been developed as shown in FIG. 3.
The electric-field sensor 300 includes a laser luminous source 131, an electric-field probe 132, an optical waveguide type modulator 133, a minute dipole 134 that consists of metal, and an optical receiving unit 135.
Since the electric-field sensor 300 is configured only by dielectric materials, except for the minute dipole 134, it is capable of measuring the electric field with a precision that is higher than the electric-field detecting methods that use the high resistance wires.
Nevertheless, since the short dipole is used according to the electric-field measuring method using the electric-field sensor 300, wherein the optical waveguide type modulator and the laser beam are used, the disturbance remains, although the disturbance becomes smaller than in the case of the electric-field measuring methods using the high resistance wires. Further, since the probe for detecting the electric field, or a 3-dimensional electric-field sensor, is moved in the liquid phantom for measuring SAR, the liquid (a phantom solvent) is agitated, and noise is generated by vibration of the probe or sensor. If a time until the solvent settles into a steady state is waited for in order to avoid the noise, measurement will take a long time. If two or more electric-field sensors are arranged in two dimensions or three dimensions in the phantom in order to shorten the measuring time, the aggregate of the sensors (short dipoles) will behave as a conductor, and will generate a great disturbance to the electromagnetic field to be measured. Consequently, a SAR distribution that is different from actual may be measured, which is a problem.